This invention relates generally to the formation of resist masks and more particularly to a process for forming different resist mask patterns on integrated circuit substrates using a single exposure and multiple development steps.
The application of photolithography to the manufacture of microminiaturized integrated circuit components is well known in the art. A layer of resist material, which usually comprises a polymer with additives such as, for example, radiation sensitizers, plasticizers and adhesion promotors, is coated onto the substrate. The substrate can be either a semiconductor wafer from which integrated circuit chips are formed or a module used to support and interconnect the semiconductor integrated circuit chips. The resist layer is exposed patternwise to electromagnetic radiation such as, for example, light, gamma rays, x-rays, electrons, etc. in order to change the solubility of portions of the resist layer. The resist layer is developed with solvents which remove the more soluble portions of the layer and uncover parts of the substrate for processing. The substrate is then selectively treated by etching or deposition processes as is conventional in semiconductor component manufacture. It is often necessary to conduct such treatments in successive steps so that different portions of the substrate are exposed for each treatment. For example, a first resist layer is patterned, the exposed portions of the substrate processed, and the first resist layer is removed; the substrate is then coated with a second layer of resist, a different pattern is formed in the resist, which pattern must be carefully aligned with respect to the previously processed areas of the substrate, and the uncovered areas of the substrate processed. The second resist layer is removed and additional resist patterns are formed, as necessary, with each pattern having to be carefully aligned with all of the proceding patterns so that an operable device is produced. As the degree of miniaturization increases, the alignment problems also increase with a consequent decrease in yields of usable product. We have now discovered a process whereby the number of alignment steps is reduced.